Method of and apparatus for controlling the performance of a d.c. magnetohydrodynamic generator

ABSTRACT

The present invention relates to a method of and an apparatus for controlling the performance of a D.C. magnetohydrodynamic (MHD) generator. The invention consists in that the performance of the MHDgenerator is controlled by means of maintaining the preset value of its electrical load factor, to which end said apparatus performs in succession three functions: SHAPES A CONTROL SIGNAL TO PERIODICALLY VARY VOLTAGES ACROSS THE ELECTRODES OF THE MHD-generator in a discrete manner, DETERMINES CHANGES OF THE MDH-generator active power within every time interval equal to the cycle of discrete variations of voltages across the electrodes and SHAPES A CONTROL SIGNAL ACCORDING TO THE ACTIVE POWER CHANGE WITHIN SAID TIME INTERVAL TO VARY VOLTAGES ACROSS THE ELECTRODES OF THE MDH-generator so as to maintain the preset electrical load factor.

FI 8532 ER 3q2732a549 United States Patent 1 1 3,792,340 Sheinkman et al. Feb. 12, 1974 METHOD OF AND APPARATUS FOR Primary Examiner-D. F. Duggan CONTROLLING THE PERFORMANCE OF A Attorney, Agent, or Firm-Holman & Stern D.C. MAGNETO'HYDRODYNAMIC GENERATOR 5 ABSTRACT [76] Inventors: Vladislav Solomonovich Sheinkman, The present invmtion relates to a method of and an Angarskaya ulitsa 61 kv Sergei apparatus for controlling the performance of a DC.

lllarionovich Pischikov, Angarskaya Q9hdr ami9( i ulitsa, 6l, kv. 20; Boris Nikolaevich The invention consists in that the performance of the Sergeenkov, Federativny prospekt, MHD-generator is controlled by means of maintaining 42, kv. 10, all of Moscow, U.S.S.R. the preset value of its electrical load factor, to which [22] Filed: Sept. 27 1972 grllldcfitalii apparatus performs in succession three [21 App]. No.: 292,805 shapes a control signal to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner,

[52] U.S. Cl. 322/7, 310/11 determines changes of the MDH generat0r active {gill power within every time interval Equal to the I 0 ea c cycle of discrete variations of voltages across the [56] References Cited electrodes UNITED STATES PATENTS shapes a control s gnal according to the active power change within said time interval to vary voltages 3,524,086 8/1970 Lmdley 3lO/ll across the electrodes of the MDH generator so as to 36l778l 1 1/197! Rosa 310/1 maintain the preset electrical load factor 3,479,537 ll/l969 Jenny et al 310/11 6 Claims, 26 Drawing Figures PATENTEDFEBIZW 3.792.340

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SHEET lSUF 15 0,5 I 150 05 i 0,4 50 j METHOD OF AND APPARATUS FOR CONTROLLING THE PERFORMANCE OF A 11.0. MAGNETOHYDRODYNAMIC GENERATOR The present invention relates to electric power engineering and, more precisely, to DC. magnetohydrodynamic (MHD) generators and in particular to a method of and an apparatus for controlling the performance of such an MHD-generator.

Known in the prior art is a method of controlling the performance of an MHDv-generator according to which the process of adjustment is effected by varying the voltages across the electrodes of the generator, said process consisting in maintaining either a constant voltage (voltage regulation) or a constant current magnitude (current regulation).

The regulation level in this case is changed manually.

This method of controlling the performance of an MHD-generator, however, fails to ensure the required energy characteristics to improve the power performance of the MHD-generator.

The manual adjustment of regulation levels performed separately for every pair of electrodes in the course of the MED-generator operation is far from rational, since it results, first of all, in that the electrical load conditions are optimized with a considerable delay.

The object of'the present invention is to provide an other method of controlling an MHD-generator which would ensure that the effective conditions of its load are maintained, as well as to design an apparatus to.

carry this method into effect.

The invention is based upon the concept of controlling the performance of an MHD-generator in a way that would ensure that the preset value of the electric load factor w is maintained. However, it must be borne in mind that to maintain the preset value of the electrical load factor automatically, which constitutes one of the major conditions for the MHD-generator operation in the "equired and especially in the optimum mode, is a relatively complex problem. The difficulty encountered here lies in the fact that, though the parameter 11;, Ue/Ee where U is the voltage across the electrodes of the MHD-generator, and

E, is the electromotive force, is simple, the value of the electromotive force should be determined correctly. As it is known 12.: l [VB]rly 2) where y and y are the coordinates of the electrodes along the Y-axis,

V is the velocity of the plasma flow in the channel of the MHD-generator and B is the magnetic induction.

The value ofthe electromotive force varies due to the fact that changes of the load current cause proportional changes of the pressure in the plasma flow, which results in the increase of its velocity due to the growth of the specific volume.

A set-up which would allow continuous direct mea-. surements in this or that way of the plasma velocity in separate sections of the MHD-generator channel, with the results being introduced into the control circuit together with the respective values of the magnetic induction and the gap between the electrodes, is not quite feasible. In addition to technical problems involved in the continuous measurement of the velocity at many points, it is necessary to take into account the errors caused by the non-uniformity of the velocity field in the channel with the variable cross section and the effect of averaging currents produced by different voltages between electrodes along the channel. Thus, it was found necessary to find convenient and feasible methods of obtaining continuous information on the magnitude of the induced electromotive force and the respective electrical load factor. Since to achieve the above object of the invention it was required to ensure that the effective mode of the MHD-generator should be maintained, the value of the MHD-generator total power, which is the most important parameter of the latter, has been assumed to serve as the principal control criterion which ensures that the electrical load factor becomes stable.

Since the maximum power delivered by an MHD- generator is obtained when the electrical load factor in all electrodes is v, =0.5, it has been found possible to use the derivative of the total power of the MHD- generator to continuously monitor the value of the electromotive force induced in the plasma flow between the electrodes.

Thus, to achieve the object of the invention the problem as stated above has been solved by the provision of a method for controlling the performance of DC. MHD-generator by varying the voltages across the electrodes of the latter which, according to the invention, consists in that the required value of the MHD- generator electrical load factor is preset, control signals to periodically vary voltages across said electrodes in a discrete manner are shaped, the change of the MHD- generator active power is found for every time interval equal to the period of the discrete voltage variations across the electrodes and then according to the change of the active power within said time interval, a control signal is generated to vary voltages across the electrodes of the MHD-generator so as to maintain the preset electrical load factor.

In the specific and preferred embodiment of the invention, as related to the method of controlling the performance of a DC. MHD-generator coupled with an A.C. mains, control signals to periodically vary voltages across the electrodes of the MHD-generator in a dis crete manner are shaped at a frequency which is twice as low as that of the A.C. mains, while the change of the active power during every time interval equal to two cycles of the A.C. mains voltage is determined by means of converting the integral of the active power within the cycle of the A.C. mains voltage into a power pulse proportional to this integral and equal to the difference between two successive pulses following each other and constituting a pair.

In the specific and preferred embodiment of the invention it is also expedient that the controller for adjusting the performance ofa D.C. MHD-generator coupled with an A.C. mains via a controllable converter and provided with a means for adjusting voltages across the electrodes of the MHD-generator should, according to the invention, contain a unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner, the output of the unit being coupled with the control input of said converter; an active power sensor facing said A.C. mains; a unit for the periodic and proportional converting of active power integrals into power pulses the input of which is coupled with the output of said active power sensor; a unit for determining the difference between two successive power pulses the input of which is coupled with the output of said unit for the periodic and proportional converting of active power integrals into power pulses, while the output of which is coupled with the input of said unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner.

The unit for shaping control signals to periodically vary voltages across the electrodes of the MHD- generator in a discrete manner in said controller of the performance of the DC. MHD-generator can also be designed as a switch using two thyristors and a switching capacitor which produces output signals, the input signals being fed to the control electrodes of the thyristors.

The unit for the periodic and proportional converting of active power integrals into power pulses in said controller of the performance of the DC. MHD-generator can also be built around a transistor operating in the key mode which is connected in-series with a linear choke and contains a train of a capacitor and a diode connected in series, the train being inserted between the emitter and the collector of said transistor.

The unit for determining the difference between two successive power pulses in said controller for adjusting the performance of a DC. MHD-generator can also be arranged around two capacitors serving to average said power pulses; a transistor forming a discharge loop with one of the capacitors of the diode which, together with said transistor, forms the discharge circuit of the second capacitor; and another transistor serving to charge the second capacitor.

The proposed method of controlling the performance of a DC. MHD-generator in conjunction with the respective units makes it possible, under other equal conditions, to raise the level of the electric power produced by the MHD-generator.

Other methods of controlling the electrical performance of a MHD-generator used nowadays, such as those mentioned above, which involve the maintenance of the current or the electrode voltage at the preset level fail to ensure the required electrical load factor or the maximum value of electric power under the conditions of plasma parameter variations in the channel which cannot be avoided in the course of the MHD- generator operation.

The proposed apparatus makes it possible to continuously take into account the effect produced by plasma parameter variations in the MHD-generator on the power performance of the latter, whereas the devices known in the prior art, though capable of measuring the current and the voltage, cannot respond directly to the variations of the electrical power produced by the MHD-generator. [n the proposed apparatus the major effect is obtained by means of directly determining the relative power variations which follow the preset variations of voltages across the electrodes before the optimum required value of the electrical load factor is achieved.

In fact, the proposed method and the respective apparatus make it possible to obtain the electrical load factor of an MHD-generator which is required according to the design project.

As shown experimentally, the increase of the electric power obtained due to the use of the proposed apparatus in an MHD-generator can be as high as 40-50 percent depending upon the range of possible variations of plasma parameters.

A detailed description will now be given of the proposed method for controlling the performance of a D.C.MHD-generator as well as of an embodiment of the apparatus for carrying said method into effect, with reference to the accompanying drawings, wherein:

FIG. 1 shows a simplified block diagram of a DC. MHD-generator whose performance is controlled by means of the method, according to the invention;

FIG.2 presents the power and the voltage-current characteristics of the MHD-generator;

FIG.3 is a simplified block diagram of a DC. MHD- generator coupled with an AC. mains the performance of which is controlled by means of the method, according to the invention;

FIGA shows a circuit diagram of the apparatus for controlling the performance of the DC. MHD- generator coupled with the AC. mains via a converter;

FIG.5 presents curves characterizing voltages and currents at the input and at the output of the active power sensor;

FlG.6 is a complete block diagram of the apparatus for controlling the performance of the DC. MHD- generator coupled with the AC. mains via the converter;

FlG.7 presents a complete circuit diagram of the apparatus for controlling the performance of the DC MHD-generator coupled with the AC. mains via the converter;

FlG.8 shows oscillograms of currents and voltages of the power sensor;

FIG. 9 shows the relationship between the average voltage at the output of the active power sensor and the active power on the side of the primary of the multiplewinding transformer;

FIG.10 is a diagram illustrating the operation of the unit for the periodic and proportional converting of active power integrals into power pulses;

FlGrll presents a circuit diagram of the unit for the periodic and proportional converting of active power integrals into power pulses;

FIG.12 shows oscillograms of signals at the input and at the output of the unit for the periodic and proportional converting of active power integrals into power pulses;

- FlG. 13 is a diagram of the power pulse follower/amplifier and of the unit for determining the difference between two successive power pulses;

FlG.l4 presents a circuit diagram of the 25-Hz voltage generator;

FlG.l5 shows oscillograms illustrating the operation of units 62, 63, 67 and 69;

FIG.16 is a diagram of the unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner;

FlG.l7 shows the relationship between the thyristor ignition angle and the output voltage of the pnit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner;

FIGJS presents oscillograms of voltages and currents of the unit for shaping control signals to periodically vary voltages across the electrodes of the MHD- generator in a discrete manner;

FlGS.l9 and 26 show oscillograms of voltages and currents occurring at the moment the proposed apparatus is switched on. for operation;

FlG.20 presents oscillograms of currents and voltages occurring at the moment the conductivity of the plasma in the MHD-generator channel becomes twice as high; 1

F102]. presents oscillograms of currents and voltages occurring at the moment the conductivity of the plasma in the MHD-generator channel becomes twice as low; and

FIGS. 22, 23, 25 and 26 present static characteristics of the proposed apparatus for maintaining the electrical load factor at the required level;

A better understanding of the essence of the proposed method could be secured from the following description of the simplified block diagram of a DC MHD-generator 1 (FIG.1) operating into a load 2 and having; a means 3 to adjust voltages across electrodes 4, a unit 5 for shaping control signals to periodically vary voltages across the electrodes 4 in a discrete manner; an active power sensor 6; a unit 7 for sensing variations of the MHD-generator active power within every time interval equal to the period of the discret voltage variation at the electrodes 4.

If the voltage across the electrodes 4 is' quickly changed by AU by affecting the means 3 in the respective way, there should occur a certaln increment AP of the power which can be either positive or negative, or zero. It is evident from FlG.2 that when the MHD- generator has a current-voltage characteristic of the simplest kind which corresponds to a linear currentvoltage characteristic of the electrodes with the power maximum at 11 =O.5, since for U,, 0.5 the value of 11 is proportional to U,,, we shall have AP/AU,, 0, while for U 0.5 we shall have AP/AU 0.5. Hence, in the course of controlling the performance of an MHD- generator the relative value of AP/AU represents a very precise criterion for assessing the electrical load factor.

It must be borne in mind that actual current-voltage characteristics can differ from linear ones considerably due to a number of reasons, and in this case APIAU O at U,,=0.5, which will allow the point on the powercharacteristic P=f( U,) to be used as the initial one for measuring the electrical load factor.

Assuming that the primary principle of control is the search of the position when A P/A U =O it must be borne in mind that this method of adjustment will be useful, first of all, for automatically driving the MHD- generator to perform with the maximum power even in case there are certain errors in maintaining the required distribution of voltages between electrodes along the channel of the MHD-generator having sectionalized electrodes.

The effect of these errors will consist in that there may occur certain deviations mainly at the beginning and at the end of the channel when the average electrical load factor along the MHD-generator channel is 0.5.

However, near the maximum of the power characteristic P=f(U,,) even considerable variations of the electrical load factor will produce a rather slight effect on the active power of the MHD-generator. Thus, with 11,, =().55 or 11,.=0.45 the power level will get down by only 1 percent in comparison with its level at 11,. =05, while with 11,, =0.6 or 11,.-=0.4 the power drop will be only 4 percent when compared with the level obtained at 11,. =05.

When checked experimentally, the proposed method of control proved that at AP/AU O the accuracy achieved in the course of calculations should allow the required value of the electrical load factor to be maintained within the range of 0.5fiil005, including the case when it is 0.5, which produces a reduction of power throughout the MHD-generator channel of less than 1 percent.

The above considerations make it easy to understand how the performance of the MHD-generator shown in FIG.1 is controlled.

Until the increment AU of the voltage across the electrodes 4 caused by the operation of the unit 5 con tinues producing the increment AP of the power of the MHD-generator 1 within the corresponding time interval equal to the cycle of discrete variations of the voltages across the electrodes 4, i.e., until the increment AP as determined by the unit 7 is positive, the unit 5 will affect the means 3 for adjusting voltages across the electrodes 4 so as to increase the power P.

As soon as the increment AU of voltages across the electrodes 4 causes a power reduction, i.e., as soon as the value AP as'measured within the corresponding time interval becomes negative, the unit 5 will start affecting the means 3 for adjusting voltages across the electrodes so as to increase the power again due to the change of the sign of the voltage increment AU,,.

Thus, the procedure of controlling the performance of the MHDgenerator shown in FIG.] ensures that the required value of the electrical load factor is maintained at the calculated optimum level of 1150.5.

The proposed method allows the value of the required electrical load factor to be maintained at any level different from 0.5 the optimum.

To this end the apparatus realizing the proposed method of control should contain a certain mismatch at which the power of the Ml-lD-generator would be measured with an error known a priori. If this measured power is P and the power increment is AP the control procedure will maintain the required electrical load factor 11 AP /AU which would differ from 1/, =05.

Consider the proposed method as applied to the MHD-generator 8 (FlG. 3) provided with sectionalized.

electrodes 0 9 and connected, via gateconverters l0 10 using thyristors and via a multiple winding transformer Ill having secondary windings 12, 12

and a primary winding 13, to a three-phase electrical mains 14.

The performance of this MHD-generator, according to the proposed method, is controlled with the help of an active sensor 15; a unit 16 for shaping control signals to periodically vary voltages across the electrodes 9 9 in a discrete manner the output of which is connected to control electrodes 1'7 17 of the thyristors; a unit 18 for the periodic and proportional converting of active power integrals into power pulses the input of which is connected to the output of the sensor 15', a

unit 19 for determining the difference between two successive power pulses the input of which is connected to the output of the unit 18 and the output of which is connected to the input of the unit 16.

Consider the process of controlling the performance of this MHD-generator.

The direct current flowing through the electrodes 9, 9 of the MHD-generator is converted into an alternating current by the gate converters l0, 10 using thyristors. The alternating current is fed to the secondaries 12 -12 of the multiple-winding transformer Ill the primary 13 of which is connected to the electrical mains 14. A signal proportional to the active power from the sensor 15 is applied to the input of the unit 18 which integrates the power value during one cycle of the AC. mains voltage so as at the end of every cycle it produces a power pulse proportional to this integral. The unit 18 is designed so that the difference between the amplitudes of the two succissive power pulses is proportional to the difference between the values of active power passing via the multiple-winding transformer 11 within the two successive cycles of the AC. mains voltage.

The signal proportional to this difference between the amplitudes of the two successive power pulses is shaped at the output of the unit 19 to be fed to the input of the unit 16.

In the course of operation small discrete variations of voltages across the electrodes 9, 9 occur continuously between the cycles of the A.C.mains voltage. In other words there is always either a positive or a negative increment AU of the voltage across these electrodes caused by corresponding slight variations AB of the values of the ingnition angle 3 characteristic of the thyristors used in the gate converters 10, I0

Voltages across the electrodes 9 9,, will change at the moments when the current flowing through the primary 13 of the multiple-winding transformer 11 crosses the zero line passing from a negative to a positive value.

The sign of the electrode voltage increment will change in case the power within the second cycle drops below the value observed during the first cycle, i.e., the change of the voltage is an unfavorable phenomenon from the point of view of approaching the required value of the electrical load factor corresponding to the optimum of the power characteristic P=f(U As long as the power increments are positive there will be no change in the sign of the voltage increment at the electrodes and successive increments A U, of voltages across the electrodes will result in the shift of the operation point towards the maximum of the power characteristic.

When the operation point reaches the area of the maximum of the power characteristic the performance of the MHD-generator becomes quasi-stable, i.e., the sign of the electrode voltage increments A U, starts alternating incessantly with every two cycles of the AC. mains voltage, but due to the fact that the positive and negative voltage increments A U which follow one another and constitute about 2.5 percent of the total value, are equal, the voltages across the electrodes remain practically unchanged having a ZS-Hz component at the AC. voltage whose amplitude isonly 1.25 percent of the average value, These voltage fluctuations cause power variations at the frequency of 25 Hz with amplitudes of only l.5 10' of the average value.

The detailed description of the essence of the proposed method of controlling the performance of a D.(.. MHD-generator will now be followed with considerations regarding devices to realize this method beginning with the simplest one designed in accordance with the simplified diagram of FIG.4 which corresponds to the DC. MHD-generator coupled with the A.C. mains via gate converters and shown in the form of a simplified block diagram in FIG. 3.

An active power sensor 15 is connected so as to face the AC. mains. It contains a current transformer 20 the primary 21 of which carries an alternating sine current to be measured. The instant values i of this current are determined through the amplitude values I,,,,, the circular frequency w and the time 2 according to the formula.

i, =1, sin wt The active power sensor 15 is provided also with a voltage transformer 22 the primary 23 of which is fed with the sine voltage to be measured. The instant value u, of this voltage at every time moment t is determined through the amplitude value U,,,,, the circular frequency m and the phase angle 4) according to the formula:

Connected to two similar secondaries 24 and 25 of the current transformer arranged in a circuit with a zero point via transistors 26,27,28 and 29 is a load resistor 30 producing a voltage drop which is proportional to the active power due to the fact that the transistors are controlled by a voltage arriving from the voltage transformer.

The voltage transformer 22 has four secondaries 31, 32, 33 and 34 which are coupled with the emitter-base junctions of the transistors 26, 27, 28 and 29 via resistors 35, 36, 37, and 38. In case the phases of voltages across the windings of the transformers 20 and 22 are properly adjusted the resistor 30 will produce a voltageu the shape of which together with those for the current 1', and the voltage u are shown in FIGS. The average value of the voltage across the resistor 30 is Where 1 1111/ V In other words for the given voltage sponds to the activ'fiower value it corre- 

1. A method of controlling the performance of a D.C. magnetohydrodynamic (MHD) generator by varying voltages across the electrodes of the latter, said method comprising the steps of presetting a required value of the MHD-generator electrical load factor, generating control signals to periodically vary voltages across said electrodes in a discrete manner, monitoring the change of the MHD-generator active power for every time interval equal to the period of the discrete voltage variations across the electrodes, and shaping the generated control signals so as to maintain the preset electrical load factor in response to a monitored change of generator active power.
 2. A method of controlling the performance of a D.C. MHD-generator connected to an A.C. mains as claimed in claim 1, wherein the control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner is shaped at a frequency which is twice as low as that of the A.C. mains, while the change of the active power during every time interval equal to two cycles of the A.C. mains voltage is monitored by means of converting the integral of the active power within the cycle of the A.C. mains voltage into a power pulse proportional to this integral and equal to the difference between two successive pulses following each other and constituting a pair.
 3. A controller for adjusting the performance of a D.C. MHD-generator, coupled with an A.C. mains via a controllable converter comprising: a means for adjusting voltages across the electrodes of the MHD-generator; a unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner, the output of the unit being coupled with the control input of said converter; an active power sensor facing said A.C. mains; a unit for the periodic and proportional converting of active power integrals into power pulses the input of which is coupled with the output of said active power sensor; a unit for determining the difference between two successive power pulses the input of which is coupled with the output of said unit for the periodic and proportional converting of active power integrals into power pulses, while the output of which is coupled with the input of said unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner.
 4. A controller for adjusting the performance of a D.C. MHD-generator as claimed in claim 3, wherein said unit for shaping control signals to periodically vary voltages across the electrodes of the MHD-generator in a discrete manner is made as a switch using two thyristors and a switching capacitor delivering output singals, the input signals being fed to the control electrodes of the thyristors.
 5. A controller for adjusting the performance of a D.C. MHD-generator as claimed in claim 3 wherein said unit for the periodic and proportional converting of active power integrals into power pulses uses a transistor operating in the key mode that is connected in-series with a linear choke and contains a network of a capacitor and a diode connected in series, the network being connected between the emitter and the collector of said transistor.
 6. A controller for adjusting the performance of a D.C. MHD-generator as claimed in claim 3 wherein said unit for determining the difference between two successive power pulses comprises: two capacitors serving to compare said power pulses; a transistor serving as a discharge network for one of the capacitors; a diode combined with said transistor to form a disCharge network of the second capacitor; and another transistor ensuring the discharge of the second capacitor. 